The present invention relates to compositions comprising: (a) at least two phenolic compounds (one flavoid and one non-flavoid); (b) at least one hydrotrope; (c) at least one emulsifier; (d) a lipid-soluble antioxidant; and (e) water. The at least one hydrotrope should be present in an amount that is effective to solubilize said at least two phenolic compounds in the water phase of the composition. The at least one emulsifier should be present in an amount sufficient to create a water-in-oil or oil-in-water emulsion that is effective to solubilize the lipid-soluble antioxidant. The compositions are useful for cosmetic purposes.
The formation of free radicals is a widely accepted pivotal mechanism leading to skin aging. Free radicals are highly reactive molecules with unpaired electrons that can directly damage various cellular membranes, lipids, proteins, RNA and DNA. The damaging effects of these reactive oxygen species are induced internally during normal metabolism and externally through various oxidative stresses. UV exposure and environmental pollution can accelerate skin aging by producing free radicals in skin. Antioxidants protect cells from the damage of oxidative stress by scavenging free radicals and inhibiting following oxidation reactions. As skin ages, the endogenous ability to protect against oxidative stress declines, and makes it necessary to provide extra help to counteract oxidative stress produced both internally and externally. The topical application of antioxidants is broadly used in skin care products to prevent skin aging.
Phenolic compounds (i.e., phenols and polyphenols), the most abundant antioxidants in diet, are well known as very effective antioxidants. They have been widely studied in the prevention of degenerative diseases, particularly cardiovascular diseases and cancers. Many phenolic compounds have been formulated in nutrition supplements and consumer products. However, the solubility of most phenolic compounds is very limited, especially in water, which diminishes their applications and biological potential in cosmetics. Thus, there is a need for methods of increasing the water solubility of phenolic compounds.
Applications and biological potential of many phenolic compounds in cosmetics are limited due to their poor solubility. Various delivery systems, such as gel carriers (US application publication 20020086042), or nano crystals (US application publication 2010/0047297), or chemical modification of the polyphenols (US application publications 20090233876, 20080095866, and 20080176956) have been used to obtain better solubility of phenolic compounds. However, these approaches have drawbacks. Some are tied to specific delivery systems. Modification of phenolic compounds increases costs, the improvement of solubility is still limited, and modifications can reduce the activity of the phenolic compounds.
Other solutions to the problem of poor solubility include the use of solubilizers such as strong organic solvents (U.S. Pat. No. 5,532,012) and diterpene glycosides (US application publication 2011/0033525). Nevertheless, these solutions do not have good safety, and are not necessarily compatible with cosmetic formulations. Moreover, most of the time, when water is added to such compositions, the solubility of the phenolic compounds decreases dramatically.
Thus, there remains a need for methods for improving the water solubility of phenolic compounds, including polyphenols, for cosmetic and other uses. Further, in order to provide a more complete protection against oxidative stress to the skin, a lipid-soluble antioxidant is desirable to protect against lipid peroxidation, which helps to maintain the integrity of cell membranes. Vitamin E (sometimes referred to commercially as “tocopherol”) is an essential fat-soluble vitamin that includes eight naturally occurring compounds in two classes designated as tocopherols and tocotrienols. It is a powerful antioxidant. α-tocopherol is the most abundant biologically active form of Vitamin E. The antioxidant properties of Vitamin E mainly function at the cellular membrane level because its lipid solubility enables it to be incorporated into the lipid layer of the cell membrane. However, to incorporate a lipid or fat-soluble antioxidant like Vitamin E into a stable aqueous or water-based composition or formulation, it is necessary to create an emulsion. The emulsions described hereinafter are suitable to create stable compositions or formulations that incorporate both the water-soluble phenolic compounds, the at least one hydrotrope and the lipid or fat-soluble antioxidant (e.g., Vitamin E) for cosmetic use.
The terms “fat-soluble”, “lipid-soluble” and “oil-soluble” are used synonymously throughout this application, as are the terms “fat”, “lipid” and “oil”.